Transmit-Receive (T/R) switches have been known since the advent of radar. Some early models were substantially nothing more than a spark gap strategically positioned (electrically) in the transmission line coupling the receiver to the antenna, to prevent high power transmitted pulses to the antenna from damaging the input circuits to the receiver. From the beginning two requirements have predominated, one, low insertion loss so that the receiver's system noise factor (NF) is not seriously impaired on receive, and two, adequate protection for the receiver during transmission. In addition to further increasing the magnitude of these requirements, modern radar systems have imposed many more requirements both technically, such as higher power levels, longer pulses, faster response time, and higher frequencies; and physically, such as small size construction, microwave integrated circuit (MIC) structure, passive protection, and integral sensitivity time control.
The following patents may provide valuable background teaching in the understanding of the present disclosure. U.S. Pat. No. 2,835,867 to patentee Golden, U.S. Pat. No. 2,847,159 to Curtis, U.S. Pat. No. 2,994,789 to Gottfried, U.S. Pat. No. 3,226,661 to Garver et al, U.S. Pat. No. 3,321,642 to Peterson, U.S. Pat. No. 3,484,308 to Lesk, U.S. Pat. No. 3,529,266 to King, U.S. Pat. No. 3,605,027 to Nichols et al, U.S. Pat. No. 3,774,123 to Hume, U.S. Pat. No. 3,810,049 to Krause, and U.S. Pat. No. 3,846,724 to Maier.